Two-wire multiple telephone system.



No. 769,701. PATENTED SEPT. 13, 1904. J. W. LATTIG & G. L. GOODRUM.

TWO-WIRE MULTIPLE TELEPHONE SYSTEM.

APPLICATION FILED JUNE 6, 1903.

N0 MODEL.

NITED STATES Patented September 13, 1904.

PATENT FFICE.

ACOB IV. LATTIG, OF \VEST BETHLEHEM, AND CHARLES LANE GOODRUM,

OF PHILADELPHIA, PENNSYLVANIA, ASSIGNORS TO EASTERN TELE- PHONE MANUFACTURING COMPANY,

OF \VESlCI-IESTER, PENNSYL- VANIA, A CORPORATION OF PENNSYLVANIA.

TWO-WIRE MULTIPLE TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 769,701, dated September 13, 1904.

Application filed June 6, 1903. Serial No. 160,323. LNo model.)

To a whom, it may concern.-

Be it known that we, JACOB IV. LAT'IIG, residing in est Bethlehem, county of Lehigh, and CHARLES LANE GooDRUM, residing in 5 Philadelphia, county of Philadelphia, State of Pennsylvania, citizens of the United States, have jointly invented a new and useful Two- \Vire Multiple Telephone System, of which the following is a specification.

I Our invention relates to telephone-exchange systems, and particularly to those in which a common battery or other source of currentsupply is employed'for the purpose of furnishing energy for both transmitters and sig- 5 nals. \\e have described in a companion application hereto, executed of even date herewith, tiled June 6, 1903, Serial No. 160,322, a system of this character in which metallic circuits are employed and but two contacts are required in each spring-jack and on each 00- operating plug in the central oilice. In that system polarized relays are employed to control the line-signals, and similar polarized relays are connected to the cord-circuits to con- 2 5 trol the supervisory signals. The benefits derivable from a two-wire multiple system are fully set forth in said application, comprising, among others, the advantage of reduced size in multiple-jack panels. simplicity of wiring,

reduction in size of cable and relay-racks, and general economies, as well as a distinct gain in directness and simplicity of operation.

Our present invention is in the nature of an improvement upon the system set forth in our application referred to; and it consists principally in certain improved arrangements of relays for the supervisory circuits whereby the polarity feature is eliminated, certainty of operation is assured, and other advantages are 4 gained which will be sufiiciently evident from the description and claims.

In carrying out our invention we may use, and preferably do use, a polar relay for the line-signal, connected between one side of the line and an intermediate point between the terminals of the main battery, together with connections from one terminal to the corresponding side of the cordcircuit and from the other terminal to the other side of line, the potential d itfereuce on the cord side-as referred 5 to the intermediate bus being higher than that on the line side. The effect of this is to produce a local circuit when a plug is inserted, having a reversed direction of cur rent to restore the line-signal. In our other application referred to, as well as in our Patent No. 722,637, issued to us h'Iarch 10, 1903, we have also described polar relays in the cord to control the supervisory signals, and included in this local circuit when a plug is insorted. Current to the intermediate bus through the local circuit would light the supervisory lamp; but when a subscriber answered this would be reversed to extinguish the same. In the present case we use two 5 neutral relays, one of high and one of low resistance or number of effective turns in the winding, the low relay shunting the high relay when a large current passes to retire the signal, this occurring when a subscriber an- 7 swers, and thereby puts his line in shunt of the high-resistance line-signal. \Vhen a small current passes in the local circuit the high relay only becomes operatively energized to light the supervisory lamp, this occurring when the line is open at the subscribers station. Thus we are enabled to attain, with differences in resistance to utilize the differences in current strength, similar results to those attained by the use of polarities. 30

Our invention is illustrated in the accompanying drawing, wherein the ligure is a diagram of a system. showing two subscribers stations A and B, connected to a central otfice containing suitable connective apparatus. 5

Referring to the drawing, the substations A and B are connected to the central otfice by the line-wires 1 2 and 3 4, respectively. These stations are equipped with the usual transmitters T T, receivers R R, ringers Q Q, 9 condensers C C, and switch-hooks H H. These do not form part of our present inven- I tion and may be of any suitable type to operl ate on central-energy metallic circuits. At the central office the lines are provided with terminal spring-jacks J and J, respectively, each of these jacks consisting, essentially, of a spring and a sleeve only, the former lettered j and the latter 3'. From the spring side of the line 1 it is connected through impedancecoil I to bus-bar 5, and the same is true of the spring side of the other line, 3. The sides 2 and 4c of the respective lines are connected through the windings/of polarized relays L andL to the bus-bar 6. Each of these polarized relays is fitted with an armature normally drawn by the force of a suitable retractile spring, aided by the permanent magnetism of the field, into position to break a local circuit 8 or 9, containing a battery m or m and a signal-lamp Zor Z. When an armature of one of these relays is thrown over by current of proper direction in the coil thereof, it closes the local circuit and lights the lamp therein. Cooperating with the spring-jacks J and J in making connections between the lines are provided plugs P and P, connected by cord conductors 18 19 20 21, inductively continuous, but conductively discontinuous by reason of the inclusion therein of the condensers C C Each plug has tip and sleeve contacts 1) and p, adapted to cooperate with the springs j and the sleeves of the jacks in making connections. Across the conductors 18 and 20 the operators telephone set 0 is adapted to be bridged by the listening-key K when the latter is depressed. This key and the telephone set we have indicated conventionally in diagram only; but it is to be understood that all the required connections for current-supply, tests, &c., aremade thereto in practice, not being illustrated in detail herein because they form no part of this invention and may be varied at will.' In the conductors 19 and 21 are included the double contacts of the ringing-key K, which when operated serves to separate the plug P from the other plug, P, and connects the conductor ends thereof to the circuit 17 of the ringinggenerator G. This also is conventionally shown; Associated with the plugs are two supervisory signals Z and Z included. in the local circuits and 11, together with suitable batteries m and M the local circuits being normally open and controlled by the armatures of relays L and L respectively. The relay L is connected on one side by wire to the conductor 18 of the'cord, and on the other side to the windings of a second relay L and thence by wires 12 and 141 to the busbar 7. Similarly, the relay L is connected on one side by wire 16 to cord conductor 19 and on the other to relay L and thence by wires 13 and 14 to the same bus 7.. The relay L, by its armature (0*, controls the continuity of a short circuit or shunt 24 25 around the relay L extending from wire'l5 to wire 23.

The relay L by its armature a controls the continuity of a shunt 24 25 around relay L extending from wire 16 to wire 26. Relays L and L are wound to have a resistance of approximately one thousand five hundred ohms each and to offer a high impedance to the passage of voice or other high-frequency currents. Relays L and L are wound to about one thousand ohms each, and relays L and L are of a special design,which will now be noticed. Each of these relays L* and L has a point of division in its windings. The total resistance of the entire winding on each is about equal to that of the winding of coil I, or approximately three hundred and fifty ohms; but that portion of its windings next to the armature end of the core or cores is of only about fifty ohms resistance, the division being made in such manner as to make this the only portion effective in attracting the armature. This may be done in various'ways. We have chosen for illustration an arrangement in which a core extension a, of soft iron, is brought out between the two portions of the relay-winding and extended down so as to pivot the armature to it, thus limiting the effective magnetic circuit to the armature, the

core extension, and that portion of the core between them. The entire winding is effective in increasing the resistance and impedance of the magnet, however. The main battery used with these coils is shown conventionally at M M. It is in two divisions, the lower one, M, of, say, fifteen cells, giving approximately two volts each, and the upper one of, say, ten cells, giving two volts each, twentyfive cells in all, giving a total voltage between bus-bars 5 and 7 of fifty volts. These voltages and also the resistances given may be departed from without altering the invention; but we give those we have found suitable.

The operation of our system so described is as follows: Suppose subscriber A calls by removing his receiver R from the hook H. The line becomes closed for calling-current from the main battery M by the following path: battery M, bus-bar 6, relay L, line-wire 2, book H, transmitter T and receiver R, linewire 1, coil 1, and bus-bar 5 to battery. The relay L becomes energized by the current in this circuit and throws over its armature, closing the local circuit 8 and lighting the lamp Z. The operator perceiving the signal inserts the answering-plug P in the answering-jack J, and after depressing the key K asks the number wanted. hen the plug is inserted, a circuit is closed for battery M, as follows: battery 1W1, bus-bar 7, wire 14, coils L and L cord conductor 18, plug-contact p, jackthimble line-wire 2, and by one path back through relay L to bus-bar 6, by the other path out over the line, through the subscribers apparatus, as before, back by 'line wire 1, through coil I to bus-bar 5 and battery M to battery M. The battery M and the battery M are thus seen to be connected oppositely to re lay L, and as the potential between bus-bars 6 and 7 is higher than that between bus-bars 6 and the former prevails and the current due to the resultant potential difference at the terminals of relay L is in a direction to throw back its armature to its normal open point, as shown, in which it is aided by the spring. The current from both divisions M and M of the battery is thrown on the line to supply the subscribers transmitter, which is preferably of the high-resistance central-energy type now coming into general use. If the subscriber should return his telephoncreceiver to its hook after calling, the effect on the supervisory signals would be as follows: Current from battery M only circulating in the local circuit 1* L" L 18 2 L 6 is so attenuated by reason of the high resistance of relays L and L and there are so few effective turns on the active core end of relay L that the armature u" of the latter is not attracted and relay L does not attract its armature effectively, because the current is in the wrong direction; but relay L has a suflicient number of turns to be effective even with this attenuated current, and it attracts its armature u to close the local circuit 10, which lights the supervisory lamp indicating that the subscriber has "hung up. On the other hand, if, according to the usual procedure, subscriber A keeps his receiver off the hook until he is through talking the above current is supplemented as regards the path .11 12 L L 15 18 ,1) j 2 by the additional current permitted to flow to the substation, or, to put it in other words, the current is increased by shunting the resistance of relay L. This increased current is sutlicient to effectively energize the core of relay L, and it attracts its armature a", shortcircuiting the magnet L, which thereupon lets its armature remain retracted, leaving the lamp dark. Having ascertained the number wanted, the operator inserts the plug 1 into a multiple jack of the line, which we will suppose to be that of station 15. (She precedes this insertion by a test, description of which is omitted.) Depression of the key K then sends ringing-current to line 3 1 and calls subscriber B by agitating his ringer Q. In inserting plug I the operator has closed the circuit of battery M by way of T 1 1 13 L 26 L 16 191/1" 4: L 6, the subscribers line 3 1 remaining open at condenser C. Current in this path is attenuated by the resistance of relays L and L and fails to energize relays L but does energize relay L to attract the armature and light lamp 1 in supervisory circuit 11. This lamp remains lighted until the called subscriber answers. When he takes down his receiver from the hook, the path to his station is closed for direct current and shunts the resistance of relay L. The increased current in L due to this is sufficient to attract armature a, whereupon a shunt 2% is closed, as previously described,

around relay L and the latter releases its armature-extinguishing lamp This signalizes to the operator that the subscriber has answered. Conversation proceeds with current flowing to keep both supervisories dark, and it will be noted that this current is not waste, but serves to keep the transmitters at the substations supplied with energy. The function of the additional resistance and impedance of magnet now appears, for it serves, in conjunction with coil 1, as L* in conjunction with I, to choke speech-waves out from the battery bus-bars. Having finished their conversation, when A or B, or either of them, hang up their receivers the corresponding relays L and L" weaken and release their arniatures, breaking the short circuits around the supervisory relays L and L and again lighting both lamps I and F, or either one of them, as the case may be.

Having thus described our invention, what we claim, and desire to secure by Letters Patent, is

1. In a telephone-exchange system, subscribers lines, operators connective circuits, a common source of current, a high-resistance linerelay in each line, a low-resistance supervisory relay in connection with each connective circuit, a circuit completed when a connective circuit is connected to a line, which comprises the supervisory relay the line-relay and a portion of the source or the whole thereof, in series, and means under the control of the subscriber to open and close his line in the use of his telephone, said line constituting a shunt for current through the supervisory relay around the linerelay,w hereby the supervisory relay is controlled, substantially as described.

2. In a telephone-exchange system, subscribers lines,operators cord-circuits, springjacks for the lines and plugs cooperating therewith for the cords, a source of current, a high resistance in each line between the spring-jack and the source of current, a supervisory relay-magnet connected between each cord and the source and adapted to be brought into series with line resistance and source when a plug of its cord is inserted in a jack, together with means at each subscribers station to close a shunt-path through the line around the lineresistance to control the supervisory relaymagnets, substantially as described.

3. In a telephone-exchange system, a subscribers line, an operators cord-circuit, jacks for the line and a plug for the cord, at source of current, a high-resistance connection from the source to the jacks, a low-wound relay and a high-wound relay in series connected from the other side of the source to the cord, means whereby the high-wound relay may control a signal and the low-wound relay may control a shunt around the high-wound relay, together with means under the control of the subscriber to close his line-circuit to furnish a path of comparatively low resistance around the normal line connection from the source, whereby the high-wound cord-relay may be shunted during a connection and its signal undisplayed, but the low-Wound relay may be deenergized to restore the same and permit it to display its signal at the conclusion of a conversation and when the line-circuit is broken, substantially as described.

4. In a telephone-exchange system, a subscribers line with a terminal jack, a cord-circuit with a terminal plug, adivided source of energy having intermediate and terminal bus connections, a connection from the jack through a high resistance to the intermediate bus, a connection from the cord through a low-wound non-sensitive supervisory relay to one terminal bus, and means controlled by the subscriber to close a branch circuit from the jack through his line to the other terminal bus, whereby on the insertion of a plug the cord-relay will not be energized, whereon the closure of the line by the subscriber it will be energized, substantially as described.

5. Ina telephone-exchange system, asignalmagnet comprising a divided winding, a continuous core for both divisions of the Winding, an armature at one end of the core and an extension of the core from the point of division between the coils to the armature, together With suitable connections and sources of current, whereby for signaling purposes a portion of the Winding only Will be effective, but in developing self-inductance in the circuit the entire Winding will be effective, substantially as described.

6. In a telephone-exchange system, a subscribers line and a terminal jack therefor, a cord-circuit and a terminal plug therefor to cooperate With the jack, a source of current, a high-resistance connection from the source of current to the line and jack, a sensitive relay controlling a signal, and a non-sensitive relay controlling the sensitive relay, both being connected from the source to the cord, together With means controlled by the subscriber to close through his line a path of relatively low resistance from the jack to the source, substantially as described.

7 In a telephone-exchange system, a subscribers metallic circuit, a high-resistance signal-magnet connected to one limb thereof and an impedance-coil to the other, a divided i battery having an intermediate terminal and two end terminals of unequal potential difference with the intermediate terminal, connections from the intermediate terminal to the high-resistance signal-magnet and from the low-potential end terminal to the impedance- JACOB W. LATTIG. CHARLES Lr tNE GOODRUM.

Witnesses:

M. S. LEWIS, EDWARD E. CLEMENT. 

